TestKotlinAndroidSynthetic

For illustrating the bug in https://youtrack.jetbrains.com/issue/KT-47733

Environment

Android Studio

Android Studio Arctic Fox | 2020.3.1 Beta 5

Build #AI-203.7717.56.2031.7479365, built on June 22, 2021

Runtime version: 11.0.10+0-b96-7281165 x86_64

VM: OpenJDK 64-Bit Server VM by JetBrains s.r.o.

macOS 11.4

GC: G1 Young Generation, G1 Old Generation

Memory: 2048M

Cores: 8

Registry: external.system.auto.import.disabled=true, debugger.watches.in.variables=false

Non-Bundled Plugins: Dart, wu.seal.tool.jsontokotlin, org.jetbrains.kotlin, io.flutter

JEB 3.17.1.202004121849

The Problem

One problem we encountered was using Kotlin synthetic with RecyclerView.

In the view tree below, the RecyclerView's item view has the same id with the view in activity (No.1 TextView's id is same with No.2 TextView's id).

And in the code below, we first access the item_text view and then initialize RecyclerView. After RecyclerView has been drawn, we access item_text again and change the text color.

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_synthetic_list)

    // Access the synthetic view before recyclerview initialize
    // @+id/item_text is existing both in list item view and in outer activity layout
    item_text

    val adapter = CustomAdapter()
    item_list.adapter = adapter

    // Access the synthetic view after recyclerview initialize and change the text color
    // In Kotlin 1.4.x because of the view cache, item_text is still the outer TextView
    // But in Kotlin 1.5.x without view cache, here actually using findViewById and get the first item in recyclerView
    item_list.post {
        item_text.setTextColor(resources.getColor(android.R.color.holo_purple))
    }
}

In Kotlin 1.4.x, we got the result below as expected:

But in Kotlin 1.5.x the old code break:

We know that it's bad practice to write the code above using the same view id in different views within the same activity, but it will at great risk to upgrade Kotlin to 1.5.x as we should go through all the code to find those problems.

We hope that synthetic behaviour will keep the same as in Kotlin 1.4.x and it's easier to upgrade to 1.5.x without fully testing our code.

Reproduce Steps

Run the code using org.jetbrains.kotlin:kotlin-gradle-plugin:1.5.21
Get app-debug.apk in folder app/build/outputs/apk/debug
Decompile the app-debug.apk in Jeb and check MainActivity in package com.sheng.testkotlinversion

.method protected onCreate(Bundle)V
          .registers 4
          .param p1
          .end param
00000000  invoke-super        AppCompatActivity->onCreate(Bundle)V, p0, p1
00000006  const               v0, 0x7F0B001C  # layout:activity_main
0000000C  invoke-virtual      MainActivity->setContentView(I)V, p0, v0
00000012  sget                v0, R$id->tv_main:I
00000016  invoke-virtual      MainActivity->findViewById(I)View, p0, v0
0000001C  move-result-object  v0
0000001E  check-cast          v0, TextView
00000022  const-string        v1, "hello kotlin!"
00000026  check-cast          v1, CharSequence
0000002A  invoke-virtual      TextView->setText(CharSequence)V, v0, v1
00000030  return-void
.end method

change the plugin in file build.gradle, switch the kotlin-gradle-plugin version to 1.4.21
Rebuild and run the project
Get app-debug.apk in folder app/build/outputs/apk/debug
Decompile the app-debug.apk in Jeb and check MainActivity in package com.sheng.testkotlinversion

.method protected onCreate(Bundle)V
          .registers 4
          .param p1
          .end param
00000000  invoke-super        AppCompatActivity->onCreate(Bundle)V, p0, p1
00000006  const               v0, 0x7F0B001C  # layout:activity_main
0000000C  invoke-virtual      MainActivity->setContentView(I)V, p0, v0
00000012  sget                v0, R$id->tv_main:I
00000016  invoke-virtual      MainActivity->_$_findCachedViewById(I)View, p0, v0
0000001C  move-result-object  v0
0000001E  check-cast          v0, TextView
00000022  const-string        v1, "tv_main"
00000026  invoke-static       Intrinsics->checkNotNullExpressionValue(Object, String)V, v0, v1
0000002C  const-string        v1, "hello kotlin!"
00000030  check-cast          v1, CharSequence
00000034  invoke-virtual      TextView->setText(CharSequence)V, v0, v1
0000003A  return-void
.end method

Revert the kotlin gradle plugin version to 1.5.21
Uncomment below code in app/build.gradle

tasks.withType(org.jetbrains.kotlin.gradle.dsl.KotlinJvmCompile) {
    kotlinOptions.useOldBackend = true
}

Rerun the project and get app-debug.apk in folder app/build/outputs/apk/debug
Decompile the app-debug.apk in Jeb and check MainActivity in package com.sheng.testkotlinversion

.method protected onCreate(Bundle)V
          .registers 4
          .param p1
          .end param
00000000  invoke-super        AppCompatActivity->onCreate(Bundle)V, p0, p1
00000006  const               v0, 0x7F0B001C  # layout:activity_main
0000000C  invoke-virtual      MainActivity->setContentView(I)V, p0, v0
00000012  sget                v0, R$id->tv_main:I
00000016  invoke-virtual      MainActivity->_$_findCachedViewById(I)View, p0, v0
0000001C  move-result-object  v0
0000001E  check-cast          v0, TextView
00000022  const-string        v1, "tv_main"
00000026  invoke-static       Intrinsics->checkNotNullExpressionValue(Object, String)V, v0, v1
0000002C  const-string        v1, "hello kotlin!"
00000030  check-cast          v1, CharSequence
00000034  invoke-virtual      TextView->setText(CharSequence)V, v0, v1
0000003A  return-void
.end method

We can see that when using kotlin android plugin with version 1.5.21, there is no _$_findCachedViewById generated.

But in kotlin android plugin 1.4.21 and in 1.5.21 with old backend there is _$_findCachedViewById generated.

I have put the output apks in folder outputDebugApp and can decompile to see the differences.

shenguojun / testkotlinandroidsynthetic Goto Github PK